Process involving the distillation and fractionation of a mixture comprising hydrocarbon compounds including volatile and nonvolatile constituents



1941 T. o. WILTON ,260,071

PROCESS INVOLVING THE DISTILLATI ON AND FRACTIONATION OF A MIXTURECOMPRISING HYDROCARBON COMPOUNDS INCLUDING VOLATILE AND NONVOLATILECONSTITUENTS Filed Feb. 24, 1937 uwv ENTOR. THOMHS Ows-row WILTONFITTORNEY Patented Oct. 21, 1941 AND FRACTION ATION HYDROCARBONCOMPRISING OF A MIXTURE COM-v POUNDS INCLUDING VOLATILEAND NON VOLATILECONSTITUENTS Thomas Owston Wilton, London, England Application February24, 1937, Serial No. 127,360 In 'Great Britain February 24, 1936 2Claims.

'ents as they are separated without intermedi- 7 ate condensation andrevaporization For the sake of illustration the process will bedescribed hereafter in connection with the distillation of tar.

According to the invention'the tar, after being deprived of some or mostof its low boiling point volatile constituents by being mixed with hotmaterials having already gone through the process cycle, is caused to'circulate through a coil still with a speed which is independent of thethroughput of the plant, in this manner avoiding coking up of the coilstill, the materials issuing from the still passing through a vapour boxwhere more of the vaporised constituents separate, the pitch residue andthe ndn-vaporised heavier constituents being sent into a mixer columnwhich they enter together with any added increments of preheated newstock to be treated, the entry of the latter being thermostaticallycontrolled by the temperature of the finished product, the mixture ofpitch, non vaporised heavier constituents and additions of new stockbeing again circulated through the coil still whereby a continuous cycleis maintained, the vapours ofdistillation from the vapour box and fromthe mixer column being led without condensation to a fractionatingcolumn from which the lighter fraction is conveyed to a heat exchanger,where the new stock being fed to the vaporizer is preheated, the saidfractions being then condensed, a portion of the light oil fractionbeing returned to the head of the fractionating column underthermostatic control.

The process is carried out with the assistance of superheated steamintroduced by perforated steam pipes at the bottom of the fractionatingcolumn, but the pipes may be dispensed with by passing instead thedistilled vapours through a superheater for vapour superheating. Thevapour box and mixer column are also similarly provided with perforatedsteam pipes, the contents of the mixer column beingwarmed up, at thecommencement of the process for example, by a superheated steam coil.

In large plants two coils may be used, one to assist in the preheatingof stock to be treated and the other to complete the distillation asalready described.

Referring to the drawing, the figure is adiagrammatic view illustrating,as an example, an arrangement of plant suitable for carrying out theprocess according to the invention, which for the sake of illustration,will be supposed to" be used for distilling tar and assumed to startfrom the cold.

The tar flows from a feed tank A by means of a pipe to a heat exchangerB where (when the whole plant is operating) the vapours from aIractionating column C impart some of their heat to the incoming newstock. The new stock flows from the heat exchanger B by means of a pipeI to a mixer'columnD forming the lower portion of a vapour column, theupper portion of which is referred to'as the vapour box G. The admissionof new stock at this point is regulated by a thermostat, controlled bythe temperature of the finished product.

When starting from cold, the additions of new stock, falling downinclined weir plates provided in themixer column D, forms a body of tarat the bottom of the column, and is pumped by means. of the tar feedpump E through a coil still F and fed to a vapour box G at the top of,and forming part of, the mixer column D. The vapours formed in thevapour box are discharged by a pipe Z at the top thereof, and proceed tothe fractionating column at M while the residue or pitch in the vapourbox G travels to the bottom of the vapour box over weir plates in thelatter, and thence proceed to the mixer column D (which is integral withsaid vapour box) by means of two pipes J and H opening respectively atthe upper part and at the lower part of the mixer column D. The pitch inthe pipe J proceeds from the vapour box to the base of the mixer columnD andis controlled by means of a cook a whereby the throughput of theplant is regulated the said cock being so adjusted as to maintain thequantity of pitch flowing to the bottom of the mixer column slightly inexcess of that required for maximum throughput.

matically opened when a predetermined temperature prevails in the mixercolumn, so as to permit more tar to be admitted thereto. The added Dbeing again circulated through the coil stilland vapour box, by meansofthe tar feed pump E, in the manner already described; the pitch residuebecoming hard pitch and the vapours of the remaining volatileconstituents separating into the vapour box.

As the pump E is preferably'designed for circulating a quantity ofliquid which is ten times the normal output of the plant for the smallerinstallations, nine-tenths of the circulating material will flow intothe upper part of the column to be used for dehydration. Thetemperature, rising continuously owing to the heat applied at the coilstill F, reaches a complete distillation temperature of from 300 to 400C; in the vapour box G. At this temperature pitch will fiow down thepipes'J and H from the vapour box and all the vapours generated in thevapour box and in the mixer column during the distillation to pitch areconducted into the fractionating column C and enter the column togetherat a point M near the bottom section.

When the level of finished residue, here pitch, in the mixer column Dhas reached a definite height, owing to a sufficient quantity of pitchflowing down the lower entry pipe J, the pitch overflows out of avalve-controlled pitch outlet L provided on that pipe, only pitch beingdischarged. This may be automatically discharged without any connectionbetween the top and bottom of the mixer column. The plant is" sooperated that no pitch discharge takes place until the temperature inthe mixer column is such that the pitch discharged is a finished productsuited in every way to requirements. This is obtained by first testingthe pitch at the pitch outlet, and setting the thermostat in the mixercolumn to open at the temperature of distillation which is required.Directly this temperature is reached, an admission of tar is allowedthrough the tar admission pipe,'and this raises the, level of pitch andpartly dehydrated tar in the mixer column, and causes the pitch tooverflow by gravity. The vapours entering the fractionating column at Mcondense and form bubbling layers of condensates on the trays of thecolumn, the vapours passing over at N at the top of the columnproceeding through the heat exchanger B and away to a condenser O. Fromthe condenser O the condensates pass to a separator P where the waterand oils are automatically separated the light oil running into a lightoil receiving tank at Q. A thermostat is, provided at N, at the top ofthe fractionating column C, which thermostat can be set to allow vapoursat any temperature below a given point to be passed over through theheat exchanger B and into condensers. In order to keep this temperatureconstant, a refiux pump R is provided which returns a certain amount oflight oil from the light ,oil receiving tank Q back to the fractionatingcolumn C at the top section N thereof through a light oil return tank bplaced above the column. Or the pump can be avoided by disposing thecondenser O and separator P, or a second condenser and separator,

at the top of the fractionating column, and providing a gravity returnto the latter. The thermostat controls the quantity returned, and thuscontrols the temperature at the top of the fractionating column to anydegree required, this temperature being fixed and'the temperature at thepoint of entry of the vapours into the column being that correspondingto the complete distillation of pitch. The boiling point of thecondensates on the trays between these two points decreases inproportion to their distance above the point M of admission of thevapours. The liquid fractions at any given temperature can be extractedbetween these points and any required fraction can be obtained at asuitable point such as T or U. Thus at any point a fraction can beobtained by opening a plug cock (e. g. T or U) provided at the side ofeach section of the column and allowing the liquid from the section toflow away to storage, and at the same time using some of this liquid toreflux back to the column at this point to'maintain the selectivity andboiling range of the desired cut. The quantity allowed to flow to thestorage tank can' be regulated by means of a cock, so that thetemperature is kept at the requisite value, in accordance'with thefraction required at that point. The bubbling sections below theadmission point of the" vapours to the fractionating column are arrangedso as to secure as pure a residue-fraction as possible,-and this isobtained in case of treatment of some oilsby the admission ofsuperheated steam at the point V at the lower part of the column, Thesuperheated steam being supplied at a temperature of approximately 350C. tends to release any lighter products which may be held in suspensionin the section of the column below the admission point M of the vapours,driving them upwards and leaving the residue fraction comparativelypure. 'By this method of separation any number of fractions of anydegree of purity can be obtained with fine limits by elaboration of thefractionating column. Very little water is required at the condenser asthe heat exchanger has a considerable condensing eifect upon the vapourspassing over from the column. The whole of the heat of distillation isthus employed in' the fractional separation of the products. In the caseof some liquids, heat exchangers may be inserted in the circuit of thetwo pipes from the vapour box. A superheated steam coil W is provided atthe bottom ofthe mixer column which can be used for warming up saidcolumn, also a perforated pipe V" for liberation of products by means ofopen steam at this point. A further perforated steam pipe X is providedat the base of the vapour box for similar purposes, so that hard pitchcan be obtained at a lower distillation point by injecting open steamthrough the perforated steam pipe at the base of the vapour box. Asuperheated steam" coil Y is placed in the bricksetting of the coilstill, so as to produce superheated steam for the plant, utilising someof the waste heat of the still.

It will be seen that the plant consists in the combination of a tardistilling plantworking on scribed above, vapours are collected at atleast two points: (1) on entering the mixer column D and (2) in thevapour box at G. Y

If desired, a pitch tower adapted for use with highly superheatedsteamand a condenser, may be fitted to the pitch outlet of the mixer.column, so that pitch of varying grades of hardness may be obtainedwithout interfering with the working of the fractionating column, byvarying the quantity of steam used in the tower. Vapours may still beextracted from the pitch at this point, which constitutes a third pointwhere vapours are collected.

The plant as it is arranged is self-operating. The thermostat arrangedas shown admitting the tar to be treated according to the temperaturesat which the plant is to be worked does not permit of excessivetemperatures. Should the temperature fall below the distilling point, nodischarge at L of the finished product would take place. Thus, with agas fired still the plant is self-operating; and with a hand firedfurnace the plant is self-operating and fool-proof, provided theoperator fires the still at reasonable intervals.

The pump E circulates material through the coil still, the vapour box,the mixer column, and back again in a closed circuit, and the tar to betreated is admitted in regulated quantities by the thermostat. Theoutlet or discharge of the plant will depend upon the level and thequantity of finished products in the mixer D. The faster the pump E isworked the greaterwill be the quantity of distillates which will bedischarged from the mixing column D through pipe Z and the less will bethe amount of vapours which will be discharged from the vapour box Gthrough the pipe Z.

When pitch according to a particular specification is not obtained bystraight distillation, due either to specific gravity, viscosity or freecarbon, this can be corrected by means of air blowing for effectingpolymerization of the constituent hydrocarbons in the tar. A small aircompressor or blower, with or without an air heater fitted in ting ofthe coil still, so, that thewaste'heat at from 400 C.-500 C. circulatesaround the melter the pipe still setting, is fitted to supply a quantityof hot air to the point X in the vapour box, and

the air and vapour carried off passes through the.

condenser, and the condensates are sent back to the column, while thecirculated pitch becomes oxidised and thickens, and its carbon contentsand viscosity increases. Alternatively, air blowing may be performedafter the pitch is discharged at the discharge valve L. This system canalso be used when bitumen is added to the column, and the resultantviscosity and free carbon adjusted to very wide ranges.

The revivification of wash oils can also be carried out by the processaccording to the invention.

When this oil has been passed through a benzol plant a number of times,and it has become charged with gums and other heavy oils which cannot beeasily removed by steam distillation; this oil can be completelydistilled off by the process, without driving off any vapours, and theresidues run away to the tar well or used for burning on the fires.

Debenzolising gas oil can also be carried out by this process, but thisis only of advantage where revivification of wash oil, with, possibly,tar dehydration is contemplated.

When bitumen mixtures or emulsions are required, the process can beeasily adapted for this purpose. In the case of bitumen mixtures, abitumen melter is installed in the brickwork setand melts a suflicientquantity of bitumen for a continuous run throughout the day. A smallfiow indicator is inserted in the pipe leading from the melter, and thebitumen is carried by gravity to a point in the mixer column. Fallingdown cascade fashion inthemix'e'r column, it becomes mixed with thedehydrated tar on its wayto' the bottom. The pump, which is circulatingthe material five or six times around the circuit before it isdischarged, thoroughly mixes the tar and bitumen, and the dischargefrom'the plant is an efficient bitumen mixture.

With regard to emulsions, it has been described how bitumen can beadded, and, of course, any other liquids can be similarly added.Emulsions [can be provided, and, in fact, are partially provided, by thevery working of the process. The scheme can be completed by theinstallation of a small mill at the outlet point of the finishedproduct.

What I claim is: V

1. A process involving the distillation and fractionation of a mixturecomprising hydrocarbon compounds, including volatile and non-volatileconstituents, which consists in continuously circulating partly treatedstock'and added increments of new stock through apparatus includingheating means adapted to raise it to and maintain it at a predeterminedtemperature such as to vaporize all of the compounds which it is desiredto separate from the residue; feeding increments of new stock to thepartly treated stock being circulated through the aforesaid apparatus,after the separation of vapors therefrom, whenever the temperature ofthe treated stock would otherwise be caused to exceed the aforesaidpredetermined temperature; mixing the new stock with the highly heated,treated stock to effect an initial volatilization of its lighterconstituents; continuously conducting the lighter vapors separated fromthe new stock and the heavier vapors separated from the re-treated stockaway from the residue material and assembling them in a single body ofvapors of various compounds each volatile at its own characteristicboiling-point; the vapors in the body being permitted to rise from anadmission zone, maintained at an approximately uniform maximumtemperature as a result of the constant supply from the aforesaidvaporizing apparatus, to successive zones of higher level and ofgradually decreasing temperature, and such of them as may fall below apredetermined minimum temperature being permitted to separate from themain body at the zone of highest level and of lowest temperature;condensing vapors at various zones of the composite body of volatilizedcompounds to produce distillates of boiling-point characteristicsdependent upon the temperature of the vapors at the respective zones ofcondensation; withdrawing the respective distillates as formed andproviding for an outfiow of a part of the residue of the stock treatedin the circulating system from which the desired distillates have beenextracted at a rate dependent upon that of the introduction of new stockirrespective of the rate of circulation through the heating means.

2. A process for distilling tar, comprising distillable oils andresidues, by maintaining a pool of material consisting of a mixture oftopped fresh charge and residual materials in the lower portion of amixing column, circulating the material from said pool through a heatingcoil and heatingvit therein to a high temperature, discharging theheatedimaterial' from said coil into a separator wherein separation ofvapors from residues occurs, withdrawing a stream of residues from saidseparator and passing it directly into the pool in the lower portion ofthe mixing column, withdrawing a second stream of residues from saidseparator, and passing it into the upper part of said mixing column,feeding a fresh vapors.

THOMAS OWSTON WILTON.

